John Grey is the father of founding X-Men member, Jean Grey. John was employed as a history professor at Bard College in Annandale-on-Hudson, New York. During the Inferno storyline, John was temporarily transformed into a demon by the Goblyn Queen, a clone of their daughter, Jean.
After the death of her daughter, Sara Grey-Bailey, and possibly her husband Paul, Dr. Grey and his wife Elaine took care of their grandchildren, Gailyn and Joey. When Operation: Zero Tolerance occurred, John was aided by Nate Grey, who ironically is an alternate version of his grandson, Nathan Summers, in saving his grandchildren, Joey & Gailyn.
He was the first of the Greys killed by the Shi'ar Death Commandos. He has been noted as being the carrier of the X-Gene that has granted Jean and the Bailey children their mutant powers.